The present invention relates to elevators, and more particularly to an apparatus well-suited for controlling a D.C. or A.C. elevator or a hydraulic elevator.
In general, elevators can be classified depending upon their drivers, into a D.C. or A.C. elevator which employs a D.C. or A.C. motor and a hydraulic elevator which is driven through a hydraulic mechanism by an electric motor. Further, depending upon their uses, they can be classified into a passenger elevator, a freight elevator, an automobile elevator and any other special elevator.
Since any of these elevators has the peculiar property of being for controlling vertical traffic, importance is attached to the precision of floor arrival besides the safety. In the case of the elevator, an inferior floor arrival precision appears as the vertical difference or level difference between a floor and a cage, and the difference hinders getting on and off.
In order to attain a high floor arrival precision, there has been usually adopted a system wherein during deceleration, the driving motor is controlled using as a desired control value a velocity command which is determined by the relationship between a distance to a target stopping position and a velocity.
With this system, however, it is difficult to attain a satisfactory floor arrival precision, and many improvements have been proposed and adopted.
As a typical one of them, a system wherein the position of the cage is directly and continuously detected near a stopping floor, and wherein the cage is operated at a small velocity on the basis of the detected position in the vicinity of the stopping position has been adopted for a long time especially in the D.C. elevator.
Regarding the A.C. elevator in which it is difficult to generate such a small velocity, it has been known to adjust the deceleration starting point of the elevator in dependence upon the load of the cage because this load affects the floor arrival precision. Besides, it has been proposed in the specification of U.S. Pat. No. 4,319,665 that a braking or driving torque corresponding to the load is generated in the vicinity of the stopping position, thereby to make more improvements.
Regarding the hydraulic elevator, as has been known from the specification of U.S. Pat. No. 3,530,958 by way of example, the floor arrival precision fluctuates greatly depending upon the temperature of oil, and hence, an improvement keeping the oil temperature constant is made.
Meanwhile, in recent elevator controls employing a digital computer, it has become possible to detect the position of the cage by counting pulses which are generated in proportion to the travel of the cage, and it has become possible to expect more enhancement in the floor arrival precision. In such system, the detection precisions of the cage position and each floor position have direct influence on the floor arrival precision, and it is therefore desired to enhance the detection precisions. As one of such improvements the specification of U.S. Pat. No. 4,387,436 has proposed a system wherein using a digital computer, the position of a cage is detected without being affected by the wear of an equipment or the elongation of a rope, whereupon an elevator is controlled. In addition, the specification of U.S. Pat. No. 4,367,811 has proposed a system wherein the position of each floor is detected at high precision, and an elevator is controlled using the floor position and a cage position which is obtained by counting the pulses.
All the elevators have been improved in the floor arrival precision by these systems, but more improvements are desired in view of the importance thereof.